GB1339455A - Method for purification of isoprene - Google Patents

Abstract

1339455 Isoprene TAKEDA YAKUHIN KOGYO KK 19 April 1971 [4 Feb 1970] 20801/71 Heading C5E Isoprene is recovered by a process comprising: (i) contacting a reaction mixture of isobutylene and formaldehyde with water to dissolve out the formaldehyde; (ii) contacting the remaining gaseous mixture of isoprene and isobutylene with an oily substance, obtained as a by-product of the reaction of isobutylene and formaldehyde, in a distillation column at a bottom temperature of not less than 80‹ C. and a top temperature of not more the 50‹ C.; and (iii) subjecting the material obtained from the bottoms of the column to further distillation whereby isoprene is recovered as a distillate. The oily substance which boils at 90-200‹ C. and comprises C 8 - C 10 unsaturated hydrocarbons may be separated from the aqueous formaldehyde solution obtained in (i) which contains entrained oily substances from the reaction mixture. The bottoms of the further distillation (iii) may be recycled to (ii) as additional oily substance. The reaction mixture used as starting material for the process is prepared by reaction of formaldehyde with a large excess of isobutylene at elevated temperature in the presence of a solid acid catalyst. Catalysts used in the examples are Ca phosphate, antimony oxide, ferric phosphate and H 3 PO 4 each supported on silica gel. During the initial period of a continuous process an organic solvent such as an alcohol, hydrocarbon an halogenated hydrocarbon, may be added with the oily substance in (ii).